RPO in this case means "option" more than "regular production", the letters will indicate the particular 2 tone
pattern of the color
numbers, and an original era color sheet will specify that, see
here, choose make and year, the 2nd sheet shows the paint #s for 533
if you're looking to touch up, rather than completely repaint, those numbers won't help, you need to take something with a good sample of the color to a paint store that can match it
Bill
